Compared to conventional light emitting diode (LED), an organic light emitting diode (OLED), a point source of light, may emit soft light which is similar to the characteristic of plane light source. The OLED can be manufactured into large area and to be transparent and made with a soft substrate to be flexible. Also, its luminance and color temperature may be adjusted. Moreover, it can be manufactured by printing to greatly reduce the manufacturing cost. Thus, the OLED has been widely developed.
However, it is an important issue to increase the efficiency of the OLED so far. The major research fields are divided into two aspects: increasing the efficiency of inner quantum and enhancing the efficiency of light extraction of lighting unite. Increasing the efficiency of inner quantum is subject to enhancement of speed rate of spontaneity radiation by electron and hole pairs. Current research proves that by adjusting the mode spatial distribution of electromagnetic wave according to Purcell effect by the electron and hole pairs, the speed rate of spontaneity radiation may be increased. In recent years, other research indicates that smaller mode volume can be generated by applying surface plasmon mode to enhance the Purcell effect. Furthermore, another experiment proves that the coupling reaction between the electron and hole pairs and surface plasmon mode with high density of states (DOS) can enhance the intensity of photoluminescence.